The present invention relates to a stent that is implanted in lumens of an organism such as a blood vessel, the bile duct the trachea, the esophagus, the ureter, and the like to cure a stenosed portion or a closed portion generated in the lumens.
To cure various diseases that are caused when blood vessels or lumens are stenosed or closed, the stent which is a tubular medical appliance is implanted at the stenosed portion or the closed portion to expand them and secure the lumen thereof. When the stent is inserted into the body from the outside, it has a small diameter. The stent is expanded (or restored to its original state) to make its diameter large at the stenosed portion or the closed portion to keep the expanded state of the lumen thereof. The stent is classified into a self-expandable stent and a balloon expandable stent in dependence on the function thereof and an expansion mode. The balloon expandable stent itself has no expanding function. After it is inserted into a desired portion inside the organism, it is secured at the desired portion. Then, a balloon disposed in the stent is inflated to expand (plastically deform) the stent by an expansive force of the balloon so that the stent is brought into close contact with the inner surface of the desired lumen.
It is necessary to perform an operation of expanding the stent of this type in implanting it to the desired portion of the organism. The self-expandable stent is made of an elastic material. The final size of the self-expandable stent is set when it is expanded. In introducing the self-expandable stent into the human body, it is folded into a small size and put into a member (plastic tube in most cases) restricting its configuration. Then the member, namely, the tube is introduced into the human body. The self-expandable stent is discharged from the tube at the desired portion. The self-expandable stent dilates itself owing to its elasticity.
The recent self-expandable stents are mostly composed of annular members formed by connecting a plurality of columnar portions to each other with a plurality of loops so that the annular members have an approximately zigzag pattern. The annular members are connected to each other with connection portions to form the self-expandable stent substantially cylindrically.
In the stent disclosed in WO96/26689, the wavy annular members are connected to each other by connectors obliquely formed.
Another type of stent is known in which adjacent snaking elements or apexes of adjacent zigzag elements penetrate into the adjacent snaking elements or the zigzag elements. This type of the stent is disclosed in WO97/32546. The stent disclosed in WO99/65421, apexes of the above-described zigzag elements are connected to each other with connectors parallel with the axis of the stent.
Still another type of stent is known in which the snaking elements or the zigzag elements form not a straight loop (loops) but a spiral (spirals). The stent of this type is composed of one or a plurality of spirals from its distal end to its proximal end. For example, the stent disclosed in WO98/30173, to keep the configuration of the stent the zigzag elements are connected to each other by connectors parallel with the axis of the stent. The stent disclosed in U.S. Pat. No. 6,013,854 is composed not of wavy annular members but of a plurality of spirals.
The connector is used in all of the above-described conventional stents to connect the elements to each other. The connector is used to connect the elements to each other, but does not contribute to the generation of an expansive force of the stent.
As a result of energetic researches of the present inventors, they have found that a construction which is composed of an element contributing to the generation of the expansive force and which has the operation of the connector allows the stent to keep an expansive force constant or more than a required degree and a favorable coverage.
It is an object of the present invention to provide a stent which does not substantially display an expansive force, does not have a connection portion having a possibility of adversely affecting the performance of the stent when the stent is curved, and has a sufficient and uniform expansive force.